Dc motor drive system for winding reel

ABSTRACT

A DC motor drive system for driving a winding reel at constant horsepower over a wide range of speeds. Two or more main drive motors and one or more auxiliary drive motors are series connected in a power supply circuit. The field circuits of the main and auxiliary motors are separately controlled in a programed manner to extend the speed range. The motor drive and associated control system are well adapted for use with rolling mills wherein the reel coils the strip leaving the last stand of the mill.

PATENTEDMAY 14 1974 SHEEI 1V f 3 RoLLING MILL w WW MM IE XN UR AD 3 V B m :W F 7 mv. l/ w Dom. m LIR ETT Alwl HAN RO C ||||I|vnu I I I I I I I I III M Greblunas i H11 3,8l1,078 [451 May 14,1974

[54] DC MOTOR DRIVE SYSTEM FOR WINDING 3,596,l55 7/l97l Huxtable 3l8/l00 REEL 823.220 6/1906 Jackson sis/98 x 3,0l8,978 l/l962 Graneau et al. 318/6 X [75] lnventor: Joseph A. Greblunas, Scotia, N.Y. [73] Assgnee: General Electric Company, Salem, Primary Examina-T: E. Lynch Mass Attorney, Agent, or Firm-Arnold E. Renner; Harold i H. Green, Jr. [22] Filed: Nov. 28, 1972 [21] Appl. No.: 310,126 [57] ABSTRACT r A DC motor drive system for driving a winding reel at [52] U.s. cl. 318/99 sis/6 mmm hms'pm'ver Over a Wide range OfSPeedS- TW [51] Int. Cl. H02 p 7/74 of more main drive motors and One of more auxiliary [58] Field of search 31s/6,98 100 drive mtfs are Serie-S fmeted i" a POWef Supply circuit.4 The field circuits of the main and auxiliary [56] References Cited motors are separately controlled in a programed man- 4 ner to extend the speed range. The motor drive and UNITED STATES PATENTS associated control system are well adapted for use :g Eushma" -f with rolling mills wherein the reel coils the strip leaveSSmal'ln l 3,275,9l8 9/1966 Taylor 318/99 mg the last Stand of the ml". 2,! 82,631 12/1939 Kenyan 318/100 X 4 Claims, 4 Drawing Figures Q w A i f ROLLIMLQ |2 Ml-LL I Fa 4 I VG UXI L IAR .I I., DRIVE MO OR I Fl E LD WB i RAT o FIB 1 |4 coNTRoL MAIN ]/'6 I VM DRIVE I MOTORS I I F IA J 1 MIA l 20 I W J.MENTEIJMM141974 3,81 1.078 sHEEI 2 nr 3y FI ELD RT IO CONTROL .1y DC MOTOR DRIVE tSYSTEM'FOR WINDING REEL BACKGROUND OF TI-IE INVENTION The present invention relates to a motor drive system i for rotating loadscsuch' as windingreels, that require high output and constant horsepower over a wide range of speeds. It is particularly well suited for driving. af

winding reel used to coil strip material processed byy a rolling mill.

Sheet'metal strip processed byrollingfmills is coiled:

at the end of'them'ill by aumotor driven winding reel. The motordrive. forithereel'must-be -designed to maintain'strip tensionandspeedrdetermined by the rollingv process. In moderntmillswheref the strip-speed maybe of the orderof '5,000 feet perminute apower. drive capacity. of they order off5,000 horsepower 'is oftenfrequired. Also, because the reelispeedmust vary in proportion to the. radiustof thecoiliwoundthereonawide speed-range is required: Thusif theU ratio of-theirnaximum to minimum radiusof the coill-isrseven to one, the. motor drive speed [range must. also be seven. to one.V Further, if the strip speed: and tension are to, remain constant, thei-horsepower output. of'thev motor drivej must remain constant over' thiswidespeed range. Since large, DC drive; motorsttypically have a rated. speed.

range'of between three and. four to one, obta-inable byI .field control, special techniques-must beresorted to forthe purpose of extendingthespeedrange of the drive system.

One such technique Vto extend the speed range, ofV large size DC motors is disclosed in Marrs U.S. Pat: No.y 3,l3'2,293, issued May 5, 1964, and'assignedlto the same assignee as the present invention. ln the Marrssystem main andauxiliary drive motors areseries connected to a power supply and mechanically coupledlto each other and to the .windingreel. Bydifferential controlofI the excitationof the two motors-theiconstant horsepower. speed range may be extended by the order of two to one. However, each motor must have'capacity equal to the required power output so that the total drive motor capacity is doubled with a corresponding increase incost. Also, because large size motors. typiv lrequired Ato synchronize ythe reel with v'mill speed changes.

i Accordingly, it isan object .of='the vpresent invention vto provide. anL improved DCmotor .'dr'ivezsystem Yfora -winding Ireel .havingf'an 1 improved .arrangement'for-obtaining consta'ntthorsepowerfover awide speed range that requires lesswtotalfmotor capacityi-than the,v Marrssystem with' consequentreduction intcost.

A further object of the invention istoprovide animproved DCf motor'drive systemflhaving the required power and speed. range V.that ireduces xfmotor loads caused by'inertia of the rotatingsystem sot that standardmotor designs;- can?l bet used.

must'beprecisely controlled. v

Astill further object of the'invention is to provide a DC motor drive and control system for a winding reel that is well adapted for use with a' rolling mill wherein tension and speed of strip material coiled on theireel Further objects and advantages of the invention will become apparent as the following description proceeds. i"

SUMMARY Briefly, in accordance with the invention an improvedDC motordriveA system with an extended constant horsepower speed range is provided wherein a pluralityH of maindrivemotors are connected in series circuit relation with eachother and with one or more auxiliary driyemotors. By separately and differentially controllingthefield excitation ofv the main and auxiliary drive motors an extended speed range is obtained.v

Bygusing a plurality of main drive motors smaller sizes can. be. used whichhaveinherently higher speed and speedV range ratings.V The, higher speed permits use of a Io'wer-gear'ratio between thedrive system and the reel vso that the. effect-of reel-inertia reflected back to the motory driveis reduced. Thehigher speed range permits use ofa smallersizefauxiliary motor or motors so that the-required total-motor capacity and hence cost is reduced. A motorlc'ontrol system designed to utilize these Characteristics advantageously is disclosed which acts to regulate, automatically, the speed and tension of strip material wound on the reel. i

- BRIEFy DESCRIPTION OF THE DRAWINGS FIG. l is a Simplified representation of a motor drive andy controlsystem for awindingreelutilizing two series-.connected main drive motors which embodies the invention.

FIG.'2 illustrates a preferred coupling arrangement for the motors illustrated in system of FIG. l.

FIG. 3 is a modified arrangement wherein two seriesconnected main: and two series-connected auxiliary drive motors are used.

FIG.'4 illustrates in greater detail a control system wheren the drivernotor arrangement of FIG. 1 may be q used tocontrol precisely the speed and tension of strip material coiled on the winding reel.

DESCRIPTION or ILLUSTRATED I EMBoDiMENrs Referring now to FIG. 1 of the drawing there is shown, in smplified form,l aDC motor drive system for drivinga winding reel ll) used to coil strip material ll leaving the-last stand of a rolling mill 12. The drive system comprises-two main DC drive motors M1 A and Mm and an auxiliary DC- drive motor M2. All three motors are-electrically connected in series circuit relation in a power supply circuit 13 energized by a source of DC- powershown as a generator 14. The main drive motors MIA and Mm have armatures Al and A2 and associated fields FM and Fwfl' he auxiliary motorMz has an armature Aaand an associated field -F2. All three motors -have rotors mechanicallycoupled together to drivethe reel i 10 through' step-up gearing 15 the connection being-indicated schematically by thedash line 16. i

The excitation currents forthe fields-FM, Fm and F2 of the-main and auxiliary drive motors are supplied by two excitation circuits-l7 and 18 which are separately controlled in a programmed manner by a field ratio control unit 19. The programming may be done by a pair of potentiometers individually controlling the two excitation circuits, the potentiometers being .jointly driven by a current-responsive motor. Such an arrangement is shown, for example, in the above-mentioned Marrs patent. lt will be noted that the main drive motor fields-*FM and vF 1,2 areparallel connected in excitation circuit 17'- so that-they are simultaneously controlled whereas the auxiliary drive motor field F2 is separately controlled by excitationcircuit 18. The field ratio control 19 is controlled by a current responsive signal supplied by lead 20 from a current responsive device such as a shunt 21 connected in the power supplylcircuit 13 so as to measure total armature current 1,2.

When the 'reel first starts to coil strip ll, the coil will have a minimum radius R, and when the coiling operation is completedit will have a maximum radius R2. If the speed of the strip is to be maintained constant, it is apparent that the motor drive system must have a ratio of maximum to minimum' speeds equal to R2/R1. Also, if constant tension is to be maintained in the strip, the horsepower delivered by the drive system will have to be constant over this speed range.

The maximum speed range obtainable from large size drive motors by field control alone4 is typically in the range of three or four to one, whereas the R2/R1 coil size ratio may be of the order seven to one. It is apparent, therefore, that a system must be provided to extend the constant horsepower speed range of the drive v system. This is accomplished by separate control of the excitation currents supplied to main and auxiliary drive motors under the programed control of the field ratio control unit 19. When the coil size is minimum at radius RI, the motor drive speed must be maximum. For this condition, the excitation of main motor'fields FM and'Fm is a minimum (weak field) and the excitation of auxiliary motor field F2 is zero. The main motors then operate at maximum rated. As 'thecoil builds up current signals on lead will call for a gradual reduction of speed. This is done by a gradual increase of excitation current in circuit 17 until the fields FM and F12 'have maximum excitation. The motors MM and Mm will then have' minimumrated or Ibase speed. As the coil continues to build up, the current in excitation circuit. 18 is ygradually increased until the excitation of auxiliaryy motor field F2 reaches a maximum rated value. At that point the coil will have reached itsimaximum size at radius R2 and the motors will be Operating at minimum speedwhich is lower than the rated speed of the". individual drive motors. This occurs because after the motor M2 is excited, the voltage VM across the 'main drive motors MM and M22 becomes less than the generator voltage VG by the amount of the voltage VA across the auxiliary motor M2. This reduction in main motor armature voltagecauses a reduction inspeed and-power. l-lowever, the net power delivered by the drive system remains constant because the power outmaindrive motor with the auxiliary and main drive motors having equal power, each motor having sufficient power in itself to drive the winding reel. The advantage of the present-invention over the Marrs system will become clear from 'the following examples of applications of the two systems. It will be assumed that the reel drive requires 5,000 horsepower with a speed range of seven to one to wind a coil of l 15.5 inches maximum diameter from a 16.5 inches minimum diameter at 5,000 feet per minute. For this coil size the minimum reel speed will be 165 RPM.

The Marrs system would require two 5,000 hplmotors having a combined capacity of 10,000 hp. Typical speed ratings for such motors at 700 volts would be 80/280 RPM, with an extended speed range of 40/280 RPM. ln this case, gears 15 would have a speed-up ratio of 165/40 or 4.13'to l.

In the system of FIG. 1, three identical motors MM, MIB and M2 could be used with each having a capacity of 275070 horsepower for awtotal combined horsepower of 7,500. Typical speed ratings for such motor's'at' '350 i volts would be l1( )/5l2v RPM withwaneffective speed range of 73.5/5 12. ln this case the gears 15 would have a speed-up ratio of l65/73.3 or 2.25/1.

ln comparing the two systems it will be noted that the system of FIG. l requires 2,500 hp less in total capacity rating with a corresponding saving in cost and motor inertia. Further, it will be noted that because the smaller size motors have inherently higher speed the speed-up gear ratio is less by a factor of 4. 13/2,25 or .1.83/1. Since the reel coil inertia torque reflected back to the motor varies as the square of the speed, the difference between the two systems is (4.13)2 (2.25)2 3.35. lnother words, with the system of FlG. l the coil and reel inertia torque reflected back into the drive system is only about one-third as large with a corresponding reduction in overload torques during acceleration and deceleration of the drive system. Due to reduced inertia torque on the drive, standard motor overloads may be used to meet the accelerating and decelerating requirements for a modern reel installation on a rolling mill.

While the drive motors MM, Mm and M2 may be coupled together in any suitable manner the arrangement of FIG. 2 hasadvantages of lower cost and reduced motor inertia. Here it will be noted that the three motor put of motor M2 is algebraically added to that of-'motorsl j MM and Mm due to the mechanical intercoupling of the motors.

' The above described motor drive system is to bedis-I tinguished from the system disclosed in the' abovementioned Marrs patent in that a plurality of seriesconnected maindrive motors is used in combination with a smaller size series connected auxiliary drive motor with simultaneous control of the fields of the main drive motors. The Marrs system utilizes only one armatures A1, A2 and A2 are mounted on a common shaft 22 and are incorporated with the associated fields FM, Fu, and F2 into a single dynamoelectric machine. This arrangement eliminates gearing that would otherwise be required to couple the motors together.

The invention is not limited to the use of two main drive motors as a greater number may be used depending on cost factors and other design considerations. Also, more thanone auxiliary drive motor may be used if desired and such a system is shown in FlG. 3. Here the system is similar to FIG. l except that two auxiliary drive motors M2A and M2B having armatures A2 and A., are used. They have associated fields F22 and F22 which are controlled simultaneously by excitation circuit 18. ln .this casev as in FIG. l, all of the main and auxiliary drive motors arel series connected in power circuit 13 andfmechanically coupled together. l-lere the excitavtion of motors M2, and M2, and, consequently, the

Inl FlG. 4 ofthe drawing, there is shownin a.one line diagram a control system for the motor drive arrangement of FIG. 1which operatesto maintain strip tension at preset values for'variousstrip speeds. This system ist well'adapted for use with airolling millwhere the speed of the strip must be synchronizedwith the speed'of: the

an exciter 24 to field 25 of power-supply generator 14.

thereby controlling the voltage and' current' of power supply circuit 13. The exciter 24 maintains the excitation level setby aninput signal. on. lead 26; Current feedback to the regulator issupplied by leadi27 from shunt' 21. i

For the purpose of adjusting the strip tension maintained by the vcurrent' regulator, there is provided atension control 28 in the form of a potentiometer which adjusts the magnitude of a reference voltage from a voltage source 29 supplied toithe current regulator vialead 30.

The rolling mill 12 is shown ashaving arpair of working4 rolls 31 drivenbyI a stand motor 32v and which feed the' processed strip 11 to the winding reel 10. Whenever there is a change in mill speed, there must also'be a corresponding change in the reelspeed to prevent looping or breaking of the strip. To provide such adjustment automatically, there is provided a pilot generator 33 driven by stand motor 32 through a drive connector 34 which produces a FPM signal indicative of the mill exit speed of strip 1'14. This FPM speed signalL is fed to the current regulator 23 via leads35, 36 and 37 to changeL the voltage and current of the power supply circuit and hence speed of the motors drivingthe reel in a direction to synchronize the reel andmill speed's. During the initial threading of the strip on the reel, there is very little current drawn by the drive motors so that additional control is'needed to synchronize the reel to mill speed. For this purpose, .there is provided a speed regulator 38 which is operative only during the start up operation. lt receives an FPM mill speed signal via lead 39 and a reel speed feedback signal via lead 40 from' a taehometer generator 39 driven by the reel. The speed control signal reaches regulator 23 by way of leads 41 and 37. After the threadng of the strip has been completed and during normal operation the speed regulator is removed from the control-circuit loop by a current sensitive relay 42 responsive to current IA in the motor armature circuit. This relay operates normally open contacts 43 and normallyclosed Contacts 44 to short out the speed regulator.

ln this system the field ratio control 19 receives a field control signal from a counter electromotive force regulator 45 hereinafter referred to as the CEMF regulator via lead 46. The CEMF regulator receives as inputs a power supply voltage signal VG via lead 47, a motor current signal 1A via lead 48 and an FPM speed signal via lead 49. lt operates to maintain a constant CEMF of ythe drive motors by adjusting the drive motor excitation in la well known manner. An adjustment potentiometer'50 is provided for initial setting of the regulator.

ln response to field control signals from the CEMF regulator on lead 46 the field ratio control 19 controls the relative magnitudes of the excitation currents in circuits 17 and 18 controlling the main and auxiliary drive motor fields FM, Fm and F; in a manner similar to that already described in connection with FlG. 1. ln this case, the control is through exciters 51 and 52 having the usual feedback circuits 53 and 54 for maintaining the excitation levels called for by the control signals supplied to input leads 55 and 56. Also, in this case, the programing of the excitation currents as between the -fields of the main and auxiliary drive motors is controlled by a coil diameter computer 57 which will now be described.

The coil diameter computer is essentially a Variable ohmic switching device which receives as inputs mill speed and reel speed signals from signal generators 33 and 39 via leads 58 and 59. During the windup of the strip ll on reel 10 the RPM of the reel as compared with the RPM of the mill rolls 31 will vary with the radiusof the coiled strip-on the reel. Therefore, the difference in these two speed signals can be taken as a measure of the diameter of the coil. The coil sizecan in turn be correlated with the desired distribution of the excitation of the motor drive system as between the main and auxiliary drive motors to achieve the desired motor speeds for constant power output. For this purpose, the coil diameter computer provides a coil size signal'on lead. 60 to control the programing of the field ratio control. v

Duringoperation of the rolling mill, the mill speeds may change Suddenly and under those conditions large accelerating or decelerating torques must be applied by the reel drive motors in order to maintain speed synchronization of the reel. To accomplish this, the'mill g lspeed signals supplied to current regulator 23 via vlead 37 are momentarily augmented or diminished, as the case may be, by the addition or subtraction to or from the speed signal of a first derivative or rate signal supplied by an inertia compensator 61. This rate signal is generated by the use of RC networks in a well known manner. Since the amount of acceleration or deceleration torque needed for reel speed tracking varies with thecoil size and hence inertia of the reel, the rate signal is varied to correspond with the total reel inertia which also includes the fixed inertia of the reel, gear and motor. For this purpose, a coil diameter signal is fed from the coil diameter computer 57 to the inertia compensator via lead 62 to achieve the desired compensation.

While there have been shown what is presently considered to be preferred embodiments of the invention, it will .be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the inven-' tion.

What is claimed as new and desired to be secured by letters patent of the United States is:

1. A DC motor drive systemfor driving at constant horsepower over an extended speed range a winding reel adapted to coil thereon 'strip material, said system comprising:

a. a plurality of DC main drive motors each having an armature and an associated field, said main drive motors having a combined horsepower sufficient to drive the reel over their rated speed range with the required tension of the strip material coiled on said reel,

b. auxiliary DC drive motor means comprising at least one motor having an armature and an associated field, v

c. coupling means mechanically coupling said main and auxiliary drive motors to rotate together and to drive the winding reel,

d. an armature circuit electrically connecting all of the armatures of said main and auxiliary motors'in series circuit relation to a source of DC power,

e. a first excitation circuit for simultaneously varying the excitation current supplied to the fields of main drive motors,

f. a second excitation circuit for separately varying the excitation current supplied to the field or fields of the auxiliary drive motor means, and

g. excitation control means responsive to the flow of current in said armature circuit for controlling the relative magnitude of the excitation currents flowing in said first and second excitation circuits to vary the constant horsepower speed of the drive sov system over a speed range greater than the rated speed range of the drive motors.

2. The drive system as set forth in claim l wherein two main and one auxiliary drive motors are utilized all of -which have the same speed range and power ratings.

the speed range of the drive system. 

1. A DC motor drive system for driving at constant horsepower over an extended speed range a winding reel adapted to coil thereon strip material, said system comprising: a. a plurality of DC main drive motors each having an armature and an associated field, said main drive motors having a combined horsepower sufficient to drive the reel over their rated speed range with the required tension of the strip material coiled on said reel, b. auxiliary DC drive motor means comprising at least one motor having an armature and an associated field, c. coupling means mechanically coupling said main and auxiliary drive motors to rotate together and to drive the winding reel, d. an armature circuit electrically connecting all of the armatures of said main and auxiliary motors in series circuit relation to a source of DC power, e. a first excitation circuit for simultaneously varying the excitation current supplied to the fields of main drive motors, f. a second excitation circuit for separately varying the excitation current supplied to the field or fields of the auxiliary drive motor means, and g. excitation control means responsive to the flow of current in said armature circuit for controlling the relative magnitude of the excitation currents flowing in said first and second excitation circuits to vary the constant horsepower speed of the drive system over a speed range greater than the rated speed range of the drive motors.
 2. The drive system as set forth in claim 1 wherein two main and one auxiliary drive motors are utilized all of which have the same speed range and power ratings.
 3. The drive system as set forth in claim 1 wherein the rotors of the main and auxiliary motors are mounted on a common shaft.
 4. The drive system as set forth in claim 1 wherein the field excitation control means acts to first supply zero field to the auxiliary motor means while the field of the main drive motors is increased through the normal speed range of said main drive motors and then acts to increase the field of the auxiliary drive motor to extend the speed range of the drive system. 